* go-gcc.cc (Gcc_backend::nil_pointer_expression): New method.
	(Gcc_backend::boolean_constant_expression): New method.
	(Gcc_backend::zero_expression): Use this->make_expression rather
	than tree_to_expr.
	(Gcc_backend::var_expression): Likewise.
	(Gcc_backend::integer_constant_expression): Likewise.
	(Gcc_backend::float_constant_expression): Likewise.
	(Gcc_backend::complex_constant_expression): Likewise.
	(Gcc_backend::struct_field_expression): Likewise.
	(tree_to_type, tree_to_expr, tree_to_stat): Remove functions.
	(tree_to_function, tree_to_block): Remove functions.
	(type_to_tree, expr_to_tree, stat_to_tree): Remove functions.
	(block_to_tree, var_to_tree, function_to_tree): Remove functions.

From-SVN: r210122